1. Field of the Invention
The present invention generally relates to a method of mounting a semiconductor chip and an apparatus for mounting a semiconductor chip.
The method of mounting a semiconductor chip can be applied to mounting of a head IC chip 11 of a hard disk device 10 to a suspension 12, as shown in FIGS. 1A and 1B, or to mounting of an IC chip 31 of a printed circuit board unit 30 to a substrate 32, as shown in FIGS. 3A to 3C.
As shown in FIGS. 1A and 1B, the hard disk device 10 has a hard disk 16 that rotates at high speed in a hermetically sealed housing 15, and a head slider assembly 19 attached to the top end of an arm 18. The head slider assembly 19 comprises a head slider 20 and the head IC chip 11 mounted on the suspension 12, as shown in FIG. 2. The head slider 20 has a magnetic head 21 formed by a thin film forming technique. The head IC chip 11 fimctions to control the magnetic head 21 by amplifying a weak signal read by the magnetic head 21, for instance. As shown in the enlarged view in FIG. 2, the head IC chip 11 has Au bumps 22 on its lower surface joined to Au pads 24 at the edge of a wiring pattern 23.
The printed circuit board unit 30 comprises a multi chip module 36 provided with a heat sink, a memory socket 38, and an I/O connector 39, all mounted on a mother board 35, as shown in FIG. 3A. The multi chip module 36 has a plurality of IC chips 31 mounted on the substrate 32, as shown in FIG. 3B. The head IC chip 31 has Au bumps 42 on its lower surface bonded to Au pads 43 formed on the substrate 32. The head IC chip 31 is also bonded onto the substrate 32 by underfill 44.
2. Description of the Related Art
FIGS. 4A to 4C illustrate a method of producing a conventional head slider assembly. The head IC chip 11 has Au bumps 51 on its lower surface. The suspension 12 has Au pads 61 on its upper surface. This head slider assembly is manufactured in the following manner.
First, the suspension 12 is fixed onto a stage 70. A predetermined amount of insulating adhesive 71 functioning as xe2x80x9cunderfillxe2x80x9d is then applied to the upper surface of the suspension 12, using a precision dispenser (not shown). The head IC chip 11 is picked up by vacuum suction of a tool 75 having a suction hole 76, and is moved onto the suspension 12. The tool 75 then presses the head IC chip 11 by a force F, and ultrasonic vibration of several xcexcm amplitude is applied to the head IC chip 11 for several seconds, as indicated by an arrow B. By doing so, the Au bumps 51 are bonded to the Au pads 61. The vacuum suction of the tool 75 is then stopped, so that the tool 75 is separated from the head IC chip 11. The suspension 12 is then moved to a heating furnace 80, so that the adhesive 71 is hardened by heat. Here, underfill 72 is formed, and the head IC chip 11 is bonded to the suspension 12 by the underfill 72. Thus, the head slider assembly 19 is completed.
The above method of producing a conventional head slider assembly exhibits at least the following disadvantages:
1. The shape of the fillet of the underfill is unstable.
The adhesive 71 functioning as the underfill is circular on the suspension 60, as indicated by a two-dot chain line in FIG. 5A. As the tool 75 presses the head IC chip 11, the adhesive 71 is pressed by the lower surface of the head IC chip 11, and is radially spread out. The spread adhesive 71 reaches the periphery of the lower surface of the head IC chip 11, and forms a fillet 90. The shape of the fillet 90 is determined by the spread state of the adhesive 71 to functions as the underfill. The spread state of the adhesive 71 varies with the applied amount and the applied position of the adhesive 71. Depending on the situation, the adhesive 71 may significantly overflow on the upper surface of the suspension 12, as indicated by reference numeral 91 in FIGS. 5A and 5B.
As the hard disk device becomes smaller, the width W1 of the suspension 12 becomes smaller. On the other hand, as more functions are added, the head IC chip 11 becomes larger in the direction of L1 shown in FIG. 5A. Accordingly, the extra portion 92 outside the mounted head IC chip 11 on the suspension 12 becomes smaller in a width W2. Furthermore, the large amount of overflow of the adhesive has an adverse effect on the on the floating characteristic of the head slider 20 with respect to a hard disk.
As for the multi-chip module 36 shown in FIGS. 3A to 3B, the large amount of overflow of the adhesive on the upper surface of the substrate 32 often hinders the mounting of other components.
2. The overflowing adhesive sticks to the tool 75.
Depending on the applied amount and the applied position of the adhesive 71, the adhesive 71 overflows onto the upper surface of the head IC chip 11 and sticks to the top end of the tool 75, as indicated by reference numeral 93 in FIGS. 6A and 6B.
When the adhesive 71 sticks to the top end of the tool 75, the suction operation of the tool 75 becomes unstable. Therefore, the top end of the tool 75 requires cleaning often. However, it is troublesome to clean the top end of the tool 75 every time the mounting of one head IC chip 11 is completed.
The applied adhesive 71 is applied in a circular pattern and spreads radially, when seen from above. Accordingly, the adhesive 71 overflows from the sides of the head IC chip 11, and reaches the upper surface of the head IC chip 11.
3. The transmission rate of ultrasonic waves from the tool 75 to the head IC chip 11 is low.
As shown in FIG. 4B, the tool 75 is brought into contact directly with the head IC chip 11. The tool 75 is made of stainless steel, and the head IC chip 11 is made of silicon. The friction coefficient xcexc1 between the tool 75 and the IC chip 11 is in the range of 0.5 to 0.7, which is relatively low. Accordingly, the transmission rate of ultrasonic waves from the tool 75 to the head IC chip 11 is low, and the bonding of the Au bumps 51 to the Au pads 61 requires a long period of time.
4. The head IC chip often deviates at the time of mounting, and the deviation results in defective mounting.
As shown in FIG. 4B, the tool 75 and the head IC chip 11 are in contact with each other.
Due to the slight orientation of the end surface 75a of the tool 75, the head IC chip 11 slightly deviates from the initial position shown in FIG. 7A in one direction of the ultrasonic oscillation (in the X1 direction, for instance) every time the tool 75 ultrasonically oscillates. Depending on the situation, the Au bumps 51 might slip off the Au pads 61, as shown in FIG. 7B, resulting in defective bonding.
In the multi-chip module 36 shown in FIGS. 3A to 3C, the pads formed on the substrate 32 each have a rectangular shape, as indicated by reference numeral 43A in FIG. 8. However, the longitudinal direction of the horizontally aligned pads 43A in FIG. 8 is equivalent to the width direction of the vertically aligned pads 43A in FIG. 8. Accordingly, the pads on the substrate 32 are not always effective in preventing the head IC chip 11 from deviating when the tool 75 ultrasonically oscillates.
In view of this, the present invention is directed to providing a semiconductor chip mounting method and device, in which the above problems are eliminated.
To solve the problems mentioned above, the present invention provides a method of mounting a semiconductor chip, comprising the steps of:
bonding bumps formed on the semiconductor chip to pads formed on a substrate by pressing the semiconductor chip, with insulating adhesive being interposed between the semiconductor chip and the substrate; and
hardening the insulating adhesive spread out between the semiconductor chip and the substrate,
wherein the bonding step includes the step of hardening a peripheral portion of the insulating adhesive spread out between the semiconductor chip and the substrate.
Since the peripheral portion of the insulating adhesive spread out between the semiconductor chip and the substrate while the semiconductor chip is pressed, a large amount of overflow of the insulating adhesive can be prevented. Thus, the fillet of the underfill can be formed in a preferable shape.
In the above method, the bonding step may further include the step of applying ultrasonic oscillation to the semiconductor chip so that the bumps formed on the semiconductor chip are bonded to the pads formed on the substrate.
Since the insulating adhesive does not overflow in large volume, the insulating adhesive can be prevented from entering the contact space between the bonding tool and the semiconductor chip. Thus, the preferable contact condition can be maintained.
In the above method, the peripheral portion of the insulating adhesive may be hardened by either light or heat.
With light or heat, the peripheral portion of the insulating adhesive spread out between the semiconductor chip and the substrate can be quickly and stably hardened.
The present invention also provides a semiconductor chip mounting device that comprises a mechanism for pressing a semiconductor chip while an insulating adhesive is interposed between the semiconductor chip provided with bumps and a substrate provided with pads, and mounts the semiconductor chip on the substrate by bonding the bumps to the pads,
the device further comprising a peripheral portion hardening unit that hardens a peripheral portion of the insulating adhesive exposed from a periphery of the semiconductor chip while the semiconductor chip is pressed.
Since the peripheral portion of the insulating adhesive spread out between the semiconductor chip and the substrate while the semiconductor chip is pressed, the insulating adhesive can be prevented from overflowing in large volume. Thus, the fillet of the underfill can be formed in a preferable shape.
The above semiconductor chip mounting device also comprises an ultrasonic oscillator that ultrasonically bonds the bumps to the pads.
Since the insulating adhesive does not overflow in large volume, the insulating adhesive can be prevented from entering the contact space between the bonding tool, which transmits ultrasonic oscillation, and the semiconductor chip. Thus, a preferable contact condition can be maintained.
In the above semiconductor chip mounting device, the peripheral portion hardening unit is either a light supplying unit or a heat supplying unit.
With the light supplying unit or the heat supplying unit, the peripheral portion of the insulating adhesive which spreads out between the semiconductor chip and the substrate can be quickly and stably hardened.
The present invention also provides a semiconductor chip mounting device that comprises a bonding tool that presses a semiconductor chip while an insulating adhesive is interposed between the semiconductor chip provided with bumps and a substrate provided with pads, and ultrasonically bonds the bumps to the pads, in which the bonding tool has basically a square pole shape and has side surfaces that are bent inward with respect to virtual flat surfaces between adjacent corners of the bonding tool.
When the bonding tool presses and ultrasonic oscillation is applied to the semiconductor chip, the insulating adhesive overflows from the sides of the semiconductor chip, and not from the corners of the semiconductor chip. The bonding tool has basically a square pole shape, and the side surfaces of the bonding tool are bent inward with respect to the virtual flat surfaces between the adjacent comers of the bonding tool. In this configuration, the overflowing insulating adhesive cannot reach and stick to the bonding tool. Accordingly, there is no need to clean the bonding tool. Also, since the bonding tool is basically the square pole, the entire semiconductor chip including the corners can be evenly pressed by the bonding tool. Thus, no cracks occur in the semiconductor chip.
The present invention also provides a method of mounting a semiconductor chip to be mounted on a substrate by a bonding tool that presses the semiconductor chip while an insulating adhesive is interposed between the semiconductor chip provided with bumps and the substrate provided with pads, and ultrasonically bonds the bumps to the pads, in which a sheet having a larger friction coefficient with both the semiconductor chip and the bonding tool than a friction coefficient between the semiconductor chip and the bonding tool is interposed between the semiconductor chip and the bonding tool, thereby carrying out ultrasonic bonding.
Since the sheet interposed between the bonding tool and the semiconductor chip has a larger friction coefficient with both the semiconductor chip and the bonding tool than the friction coefficient between the semiconductor chip and the bonding tool, the energy transmission from the bonding tool to the semiconductor chip can be carried out at high efficiency, and the bonding of the bumps formed on the semiconductor chip to the pads formed on the substrate can be completed in a short period of time. Also, less deviation occurs in the location of the semiconductor chip.
The present invention also provides a semiconductor chip mounting device comprising a bonding tool that presses a semiconductor chip while an insulating adhesive is interposed between a semiconductor chip provided with bumps and a substrate provided with pads, and ultrasonically bonds the bumps to the pads; and a means for moving and placing a sheet between the bonding tool and the semiconductor chip which exhibits a greater friction coefficient with both the semiconductor chip and the bonding tool than a friction coefficient between the semiconductor chip and the bonding tool.
Since the friction coefficients between the bonding tool and the sheet and between the sheet and the semiconductor chip are both greater than the friction coefficients between the bonding tool and the semiconductor chip, the energy transmission from the bonding tool to the semiconductor chip can be efficiently carried out by placing the sheet between the bonding tool and the semiconductor chip. Accordingly, the bonding of the bumps formed on the semiconductor chip to the pads formed on the substrate can be completed in a shorter period of time. Also, less deviation occurs in the location semiconductor chip.
The present invention further provides a substrate on which a semiconductor chip is to be mounted by ultrasonic bonding, comprising pads each having a shape that is elongated in a direction of ultrasonic oscillation applied to the semiconductor chip.
When the bonding tool applies ultrasonic oscillation to the semiconductor chip, the semiconductor chip tends to be displaced due to the orientation of the bonding tool. In the above configuration, however, the bumps formed on the semiconductor chip do not move off the pads each having a shape elongated in the direction of the ultrasonic oscillation. Thus, defective bonding can be prevented between the semiconductor chip and the substrate.